Area Forecast Discussion
Issued by NWS Raleigh/Durham, NC

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FXUS62 KRAH 250805

Area Forecast Discussion
National Weather Service Raleigh NC
405 AM EDT Sat Mar 25 2017

Bermuda high pressure will extend west into the Carolinas and VA
through the weekend. A weakening upper level disturbance will cross
our region on Sunday.


As of 400 AM Saturday...

Little change in the forecast of warm SSWly flow and partly sunny
conditions today, and mild and continued dry tonight.

The models have trended slower with the lifting of a closed upper
low now over OK, likely as a result of ridging within, and greater
spatial separation from, the main belt of the nrn stream westerlies
along the Canadian border. Nonetheless, the upper low will likely
maintain a steady, albeit slower, NEwd progression to near KSTL by
12Z Sun, as an upstream "kicker" shortwave trough amplifies through
the Four Corners region, from the CA coast this morning.

While low amplitude perturbations in SSWly flow aloft will spread E
of the main upper low and result in weak (10-20 meter) height mid
level falls over NC today, preceding sub-tropical ridging centered
over the wrn Atlantic --and associated subsidence drying and capping
influence Wwd into the Carolinas-- will continue to dominate our
weather today. RAP temperatures have performed better than other
guidance with dry adiabatic mixing through 900-850 mb in recent
days; and see no reason to deviate from this guidance that favors
high temperatures in the middle to upper 70s today.

Tonight: SSWly stirring around the wrn periphery of the sub-tropical
ridge/Bermuda high, and considerable high clouds topping probable
late-night stratus, should result in milder-than-guidance low
temperatures, in the middle to upper 50s. While glancing forcing for
ascent downstream of the lifting upper low will continue to pivot
NEwd across central and wrn NC late tonight, associated forecast
omega is centered in the mid levels where dry air from the subsident
sub-tropical ridge will be maximized. As such, it seems unlikely
that any band of upstream showers will survive and/or arrive even in
the wrn Piedmont prior to 12Z, so the forecast will be a dry one
through early Sun.


As of 400 AM Saturday...

The upper low over the southern Plains states will lift to
toward the Great lakes and weaken today through Sunday, while a
Bermuda High continues to provide a warm southerly wind over the
Carolinas. Ongoing convection in the Southern Appalachians
Sunday morning should weaken as it moves out ahead of the
primary cold front and the upper low, while becoming negatively
tilted, weakens and passes well to our northwest. Aside form the
western Piedmont, where 40-60m height falls appears to erode a
fairly stout capping inversion, the rest of central and eastern
NC remains capped by the sub-tropical ridge. Models continue to
trend drier for most of central NC, and POPs have been adjusted
down to just a chance west of US 1 on Sunday. Widespread cloud
cover and possible showers will likely hold temps back a little
in the west, but southerly flow should still allow highs to
reach the mid 70s in the east.

Models cranks out some light qpf Sunday night, but this looks
over done, and stratus looks to be the only really issue, with
mild lows in the mid and upper 50s.


As of 400 AM Saturday...

With split flow persisting over the western US, yet another
shortwave is forecast to eject east across the Mid-South Monday
and Tuesday. Better destablization is expected each day as the
low-levels continue to moisten around the Bermuda high, though
limited forcing makes it hard to see more than isolated showers
and storms on Monday. The relatively weak upper wave will cross
NC late Monday night and Tuesday, and should result in a better
chance of storms as it interacts with better instability on
Tuesday. Highs both days will be in the upper 70s to lower 80s.

The ridge aloft will then build back over the region Wednesday
ahead of another upper low moving into the central Plains.
meanwhile, a cold front is progged to push backdoor into NC
Wednesday night and Thursday on the heels, though its still
unclear how far south the front will get given the presence of
the upper ridge. the GFS is much more aggressive with the front
but also has a much more amplified northern stream flow. Temps
will be knocked back into the 60s and lower 70s, with a possible
cold air damming scenario setting up as high pressure migrates
across the Great Lakes and the aforementioned low pressure
system moves through the Midwest.


As of 215 AM Saturday...

VFR conditions are expected for most of the TAF period, with a
couple of exceptions. The first will be a chance of radiation fog
around daybreak at RWI and FAY, where winds will be lightest in
proximity to offshore high pressure, and also where surface
dewpoints around 50 degrees are maximized relative to areas to the
west. In addition, morning to midday heating of a seasonably moist
air mass around Bermuda high pressure will favor the development of
a field of stratocumulus that will initially develop around 2500-
3000 ft, and may be briefly broken at that time.

Otherwise, SSWly surface winds will increase into the 6-12 kt range
after 14Z, with occasional gusts into the teens kts, then lessen
after sunset.

Outlook: Late night-early morning fog and/or stratus, then MVFR
range cloudiness as that moist layer is heated through midday, will
be possible each day through early next week. Otherwise, a chance of
showers and associated sub-VFR conditions mainly at Piedmont TAF
sites will exist Sun, then again forecast area-wide on Tue.




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